Muscles of Facial Expression

One of the most striking contrasts between a human face and that of a rat, horse, or dog, for example, is the variety and subtlety of human facial expression. This is made possible by a complex array of small muscles that insert in the

Soleus

Figure 10.4 The Muscular System. (a) Anterior aspect. In each figure, major superficial muscles are shown on the anatomical right, and some of the deeper muscles of the trunk are shown on the left. Muscles not labeled here are shown in more detail in later figures.

Orbicularis oris

Sternocleidomastoid - Trapezius

Pectoralis minor Serratus anterior

Rectus abdominis

Transversus abdominis

Internal abdominal oblique

- External abdominal oblique

Gastrocnemius

Soleus

Figure 10.4 The Muscular System. (a) Anterior aspect. In each figure, major superficial muscles are shown on the anatomical right, and some of the deeper muscles of the trunk are shown on the left. Muscles not labeled here are shown in more detail in later figures.

Saladin: Anatomy & Physiology: The Unity of Form and Function, Third Edition

Fibularis longus

Figure 10.4 The Muscular System (continued). (b) Posterior aspect. In each figure, major superficial muscles are shown on the anatomical right, and some of the deeper muscles of the trunk are shown on the left. Muscles not labeled here are shown in more detail in later figures.

Occipitalis

Trapezius

Infraspinatus Teres minor Teres major

Triceps brachii

Latissimus dorsi

External abdominal oblique

Gluteus medius

Iliotibial band

Soleus

Fibularis longus

Figure 10.4 The Muscular System (continued). (b) Posterior aspect. In each figure, major superficial muscles are shown on the anatomical right, and some of the deeper muscles of the trunk are shown on the left. Muscles not labeled here are shown in more detail in later figures.

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

334 Part Two Support and Movement

Frontalis -Procerus -

Orbicularis oculi

Nasalis

Levator labii superioris

Zygomaticus major

Parotid salivary gland

Masseter-

Depressor — labii inferioris

Depressor anguli oris

Platysma-

Sternocleidomastoid

334 Part Two Support and Movement

Frontalis -Procerus -

Orbicularis oculi

Nasalis

Levator labii superioris

Zygomaticus major

Parotid salivary gland

Masseter-

Depressor — labii inferioris

Depressor anguli oris

Platysma-

Figure 1 0.5 Some Muscles of Facial Expression in the Cadaver.

dermis and tense the skin when they contract (fig. 10.5). These muscles produce expressions as diverse as a pleasant smile, a threatening scowl, a puzzled frown, and a flirtatious wink (fig. 10.6). They add subtle shades of meaning to our spoken words and are enormously important in nonverbal communication.

We will briefly "tour" the scalp and face to get a general idea of the locations and actions of these muscles. Table 10.2 gives the details of their origins, insertions, and innervations. All of these muscles but one are innervated by branches of the facial nerve (cranial nerve VII). This nerve is especially vulnerable to damage from lacerations and skull fractures, which can paralyze the innervated muscles and cause parts of the face to sag.

The occipitofrontalis is the muscle of the scalp. It is divided into the frontalis of the forehead and occipitalis at the rear of the head, connected to each other by a broad aponeurosis, the galea aponeurotica13 (GAY-lee-uh AP-oh-new-ROT-ih-cuh) (fig. 10.7). The occipitofrontalis moves the scalp, forehead skin, and eyebrows.

Each eye is encircled by the orbicularis oculi,14 a sphincter that closes the eye. The levator palpebrae supe-

galea = helmet + apo = above + neuro = nerves, the brain 14orb = circle + ocul = eye rioris15 opens the eye; it lies deep to the orbicularis oculi in the eyelid and roof of the orbit. Other muscles of the orbital and nasal regions—the corrugator supercilii,16 procerus,17 and nasalis18—are described in table 10.2. Muscles within the orbit that produce movements of the eye itself are discussed in chapter 16.

The mouth is the most expressive part of the face, so it is not surprising that the muscles here are especially diverse. It is surrounded by the orbicularis oris,19 a sphincter that closes the lips. Several other muscles approach the orbicularis oris from all directions. The first major muscle lateral to the nose is the levator labii supe-rioris, a triangular muscle that originates at the middle of the orbicularis oculi. Next is the zygomaticus20 minor, which originates near the lateral corner of the eye. Both of these converge on the orbicularis oris. The zygomaticus major originates in front of the ear and inserts on the superolateral corner of the mouth. The levator anguli oris originates on the maxilla and likewise inserts on the superolateral corner of the mouth. The risorius21 approaches the mouth horizontally and inserts at the junction of the upper and lower lips. From their insertions, you can probably guess that the last five muscles draw the upper lip upward and laterally in such expressions as smiling and laughing.

Along the lower lip are muscles that draw it downward. The most lateral is the depressor anguli oris,22 also known as the triangularis because of its shape. Lying deep to it and a little more medially is the depressor labii infe-rioris. Most medially, near the mental protuberance, is a pair of tiny mentalis23 muscles. Unlike the other two, the mentalis muscles do not depress the lip. They originate on the mandible and insert in the dermis of the chin. When they contract, they pull the soft tissues of the chin upward, which wrinkles the chin, pushes the lower lip outward, and creates a pouting expression. People with especially thick mentalis muscles have a groove between them, the mental cleft, externally visible as a dimple of the chin.

The muscle of the cheek is the buccinator,24 which has multiple functions in blowing, sucking, and chewing. The name literally means "trumpeter"—if the cheeks are inflated with air, compression of the buccinator muscles blows it out. Sucking is achieved by contracting the buccinators to draw the cheeks inward and then relaxing them. This action is especially important for nursing levator = that which raises + palpebr = eyelid + superior = upper

16corrug = wrinkle + supercilii = of the eyebrow

17 procer = long, slender

1snasalis = of the nose

19oris = of the mouth

20refers to the zygomatic arch

21 risor = laughter

22depressor = that which lowers + angul = corner, angle

23mentalis = of the chin

24bucc = cheek

Saladin: Anatomy & Physiology: The Unity of Form and Function, Third Edition

Chapter 10 The Muscular System 335

Frontalis

Levator palpebrae superioris

Zygomaticus major and minor

Levator anguli oris Levator labii superioris

Depressor labii inferioris

Procerus

Frontalis

Levator palpebrae superioris

Corrugator supercilii

Orbicularis oris

Depressor anguli oris

Mentalis

Levator palpebrae superioris

Zygomaticus major and minor

Depressor labii inferioris

Procerus

Frontalis

Levator palpebrae superioris

-Platysma

Chapter 10 The Muscular System 335

-Platysma

Frontalis

Levator palpebrae superioris

Nasalis

Risorius

Depressor labii inferioris

Orbicularis oculi

Orbicularis oris

Depressor anguli oris

Mentalis

Frontalis

Levator palpebrae superioris

Nasalis

Risorius

Depressor labii inferioris

Orbicularis oculi

Orbicularis oris

Depressor anguli oris

Mentalis

Figure 10.6 Expressions Produced by Several of the Facial Muscles. The ordinary actions of these muscles are usually more subtle than these demonstrations.

infants. To appreciate this action, hold your fingertips lightly on your cheeks as you make a kissing noise. You will feel the relaxation of the buccinators at the moment air is sharply drawn in through the pursed lips. The buccinators also aid chewing by pushing and retaining food between the teeth.

The platysma25 is a thin superficial muscle that arises from the shoulder and upper chest and inserts

5platy = flat broadly along the mandible and overlying skin. It depresses the mandible, helps to open and widen the mouth, and tenses the skin of the neck (during shaving, for example).

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